Public key encryption (asymmetric key cryptography) includes an asymmetric scheme that uses a pair of keys for encryption: the public key encrypts data, and a corresponding secret or private key decrypts it. For digital signatures, the process is reversed: the sender uses the private key to create a unique electronic number that can be read by anyone possessing the corresponding public key, which verifies that the message is truly from the sender. In contrast, a symmetric scheme (symmetric key cryptography) includes an encryption system in which the sender and receiver of a message share a single, common private key that is used to encrypt and decrypt a message. Regardless of whether symmetric or asymmetric schemes are at issue, the private key of either scheme is a key that should be held in confidence if the scheme is to effectively promote secure computing.